Vision Flashcards
The output neurons of the retina, the retinal ganglion cells, group together at ______.
the optic disk
____ are larger in the periphery of the retina..
Receptive fields
What happens after the 2 optic nerves converge @ the optic chiasm?
half of the axons from each eye cross to the other side and continue on as the optic tract
What do rods mediate?
black/white; light/dark vision
What does activation of transducing cause?
activation of cGMP phosphodiesterase (PDE)
What coordinates head and eye movements? Where is this structure located?
the superior colliculus; on the dorsal surface of the midbrain
These are central regions of the hypercolumns where color information is deciphered.
blobs
These cells capture photons of light and convert them into an electrical signal.
photoreceptor cells
What determines cortical wiring?
genetics
This is a .2mm wide region where acuity is the greatest.
the fovea
The period of time when the connections can be altered by visual experience is called ____.
the critical period (or sensitive period)
What is the dorsal parallel pathway?
- from V1 dorsally –> parietal lobe
- spatial vision
- passes thru the thick stripe region of V2 and thru V5
What are binocular cells sensitive to?
depth perception
Layers 1, 4, and 6 of the lateral geniculate nucleus (LGN) of the thalamus receive input from the ______.
contralateral eye
What does the postsynaptic cell release to the presynaptic cell? When can the presynaptic cell take it up?
trophic factors; only when it’s been recently active
_____ have donut-shaped receptive fields and come in on-center and off-center types.
Ganglion cells
Layers 3-6 of the lateral geniculate nucleus (LGN) of the thalamus receive inputs from the _____.
parvocellular ganglion cells
How many rods are in the human retina?
100 million
Category 4 ocular dominant cells are ____ driven.
equally (from both sides)
What do cones mediate?
color vision
What is hierarchical processing in the eye?
several cells with similar but spatially offset receptive fields converge on a higher order cell to create an altogether new type of receptive field
Beyond the lateral geniculate nucleus (LGN) of the thalamus, the axons fan out into the ______ to the visual cortex.
optic radiations
Receptive fields are larger in the ______ of the retina.
periphery
Each hypercolumn is divided into 2 parts, one half for each eye, called _____.
ocular dominance columns
What do complex cells do?
abstract for position
In the dark, the concentration of cGMP is ____, causing the nonselective cation channels to stay _____.
high; open
Layers 1 and 2 of the lateral geniculate nucleus (LGN) of the thalamus receive inputs from the _____.
magnocellular ganglion cells
What are the features of the parvocellular ganglion cells.?
object vision- color, form, detail high acuity –> fine detail small receptive fields not responsive to motion color vision (input from cones) layers 3-6 of the LGN
What are the 2 primary parallel pathways through the ascending visual system?
- the dorsal pathway
- the ventral pathway
What are the features of the magnocellular ganglion cells.?
spatial vision- motion and depth low acuity (crude) large receptive fields responsive to motion no color vision (input from rods) layers 1 and 2 of the LGN
V5 is often called the _____.
middle temporal (MT)
What is a hypercolumn?
- a microregion of V1
- 1mm
- 10,000 LGN axons
- 6 layers
Which parts of the eye provide the focusing (refractive) power?
cornea (2/3) and lens (1/3)
Name the ganglion cell type: object vision- color, form, detail high acuity –> fine detail small receptive fields not responsive to motion color vision (input from cones) layers 3-6 of the LGN
parvocellular ganglion cells
Bipolar cells always make ____ synapses on ganglion cells.
excitatory
Light –> hyperpolarize photoreceptor –> ?
less NT release
What 2 synapses in the eye are always excitatory?
- surround photoreceptors –> horizontal cell synapse
- bipolar cell –> ganglion cell synapse
This is a microregion of V1 that is 1mm and contains 10,000 LGN axons in 6 layers.
a hypercolumn
How many photoreceptors does the optic disk contain?
none
Each microregion of V1 is called a _____.
hypercolumn
Where are cones concentrated?
in the fovea
The ______ cells group together at the optic disk forming the optic nerve.
retinal ganglion
Where are horizontal cells found?
surrounding the receptive fields
These cells abstract for position.
complex cells
This is a ganglion cell excited by light in their center and inhibited by light in the periphery.
on-center ganglion cell
Layers ____ of the lateral geniculate nucleus (LGN) of the thalamus receive inputs from the parvocellular ganglion cells.
3-6
What does glutamate do to bipolar cells?
it either excites them (off-center) or inhibits them (on-center)
What does light do to rhodopsin?
causes it to activate transducin (a G protein)
If one eye is deprived from vision, what happens to its synaptic connections in the cortex?
they degenerate and disappear
Lesions in V4 can result in ______.
impairments in color discrimination
____ is the method by which light is focused on the retina by the cornea and lens.
Refraction
If light passes from one medium to another, it is ____.
refracted
Intensity corresponds to the perceptual ____ of an object, while wavelength corresponds to _____.
brightness; color
Layers 2, 3, and 5 of the lateral geniculate nucleus (LGN) of the thalamus receive input from the ______.
ipsilateral eye
What are the wavelength boundaries of the visible light spectrum and what color do they coordinate with?
400nm (blue) –> 700nm (red)
Light can be described as having ____ and ____.
wavelength and amplitude (intensity)
What are the 3 kinds of human cones?
- blue
- green
- red
What does reduced cGMP in the optic disc do?
closes Na channels –> hyperpolarization
Most of the bipolar cells in the fovea are connected directly to _____ and indirectly to _____.
direct = one kind of cone in the field center indirect = cones with a different color preference in the field surround
The optic nerves from the 2 eyes merge at the ____.
optic chiasm
What do photoreceptors release?
glutamate
What is the fovea?
a .2mm wide region where acuity is the greatest
What are blobs?
central regions of the hypercolumns where color information is deciphered
Which synapse in the eye is always inhibitory?
horizontal cell –> photoreceptor synapses
In which hypercolumn layer do LGN axons terminate?
layer 4
What is the pupil?
the opening thru which light enters the eye
Layers _____ of the lateral geniculate nucleus (LGN) of the thalamus receive input from the ipsilateral eye.
2, 3, and 5
What is an off-center ganglion cell?
ganglion cell excited by light shining in the periphery and inhibited by light shining in their center
Which synapse in the eye can either be excitatory or inhibitory?
synapses with the on- or off-center bipolar cells
The lateral geniculate nucleus (LGN) of the thalamus represents the ____ visual field.
contralateral
Light absorption causes photoreceptors to ____.
hyperpolarize
What input does the lateral geniculate nucleus (LGN) of the thalamus receive?
visual info via the optic tract
Layers ______ of the lateral geniculate nucleus (LGN) of the thalamus receive inputs from the magnocellular ganglion cells.
1 and 2
Ganglion cells have donut-shaped receptive fields and come in ____ and _____ types.
on-center and off-center
Where do ganglion cell axons end?
in the lateral geniculate nucleus (LGN) of the thalamus
The longer the period of monocular deprivation during the sensitive period, _____.
the worse the outcome
___ and ____ are located together within the same hypercolumn.
Simple and complex cells
The retinal ganglion cells group together at the _____ forming the optic nerve.
optic disk
What are ocular dominance columns?
each hypercolumn divided into 2 parts, one half for each eye
In strabismus, what happens to the bilateral eye inputs?
one eye wins everything and the other loses altogether –> monocular driving of the cells
The lateral geniculate nucleus (LGN) of the thalamus is composed of ____ layers.
6
What is retinotopic projection?
axons project in an orderly fashion to the cortex
___ tend to be found at the borders of the ocular dominance columns.
Binocular cells
What is parallel processing?
dimensions of an object are analyzed separately but in parallel, neutral systems and then are later united
What is the ventral parallel pathway?
- from V1 ventrally –> temporal lobe
- object vision
- passes thru the stripe and interstripe regions of V2 and thru V4
What do bipolar cells synapse with?
ganglion cells
What cells in the eye make APs?
ganglion cells
_____ is the process by which light is converted into a change in membrane potential by the photoreceptors.
Phototransduction
The foveal region occupies nearly ____ of the visual cortex.
1/2
How many codes are there in a human retina?
8 million
What do photoreceptor cells do?
capture photons of light and convert them into an electrical signal
retinal ganglion cells @ optic disk –> optic nerve –> optic chiasm –> optic tract –> ?
lateral geniculate nucleus (LGN) of the thalamus
What are color opponent cells?
bipolar cells that are directly connected to one kind of cone in the field center and indirectly to a different color preference in the field surround
The retina contains what 5 types of neurons?
- rods
- cones
- bipolar cells
- horizontal cells
- ganglion cells
At the chiasm, the axons from the _____ half of each retina cross over to the opposite side.
nasal
This is a ganglion cell excited by light shining in the periphery and inhibited by light shining in their center.
an off-center ganglion cell
The retinal ganglion cells group together at the optic disk forming _____.
the optic nerve
What controls the size of the pupil?
the ciliary muscles
What does reduced cGMP concentration cause?
closure of nonselective cation channels in the surface membrane –> hyperpolarization of the cell
What is an on-center ganglion cell?
ganglion cell excited by light in their center and inhibited by light in the periphery
Ganglion cells only care about ____.
contrast
Layers 1, 4, and 6 of the ______ receive input from the contralateral eye.
lateral geniculate nucleus (LGN) of the thalamus
What does PDE activation do?
hydrolyses cGMP to reduce its concentration
Name the ganglion cell type: spatial vision- motion and depth low acuity (crude) large receptive fields responsive to motion no color vision (input from rods) layers 1 and 2 of the LGN
magnocellular ganglion cells
Layers _____ of the lateral geniculate nucleus (LGN) of the thalamus receive input from the contralateral eye.
1, 4, and 6
Lesions in the middle temporal (MT) area result in ____.
impaired motion and depth perception
Category 1 and 7 ocular dominant cells are ____ driven.
monocularly
The back of the inner eye contains the ____, which is the receptive organ of the eye.
retina
Photoreceptors talk to ____ and ____ cells.
bipolar; horizontal
Synchronous activity from both eyes is necessary for ______ during development of the visual cortex.
establishment of proper synaptic connections
The output neurons of the retina, the ______, group together at the optic disk.
retinal ganglion cells
Ganglion cells have _____-shaped receptive fields and come in on-center and off-center types.
donut
These cells are sensitive to depth perception.
binocular cells
What absorbs the photon of light?
vitamin A
